Electrocatalytic Properties And Application Of Boron-Doped Diamond Thin-Film Electrode

Diamond thin film is a new electrode material that has received great attention recently because it possesses several technologically important characteristics such as large overvoltage for the anodic oxygen evolution, low background currents, an inert surface with low adsorption properties, remarkable corrosion stability. Thanks to these properties, diamond film seems to be a promising electrode material than the traditional electrode and so, it has been studied with the goal of developing applications in electro-synthesis,electrochemical water treatment,electro-analysis technology. The high overpotential for oxygen transfer enables diamond electrode to produce hydroxyl radicals and short-lived species in the anodic oxidation reaction. In this dissertation, the application of boron-doped diamond electrodes for electro-catalytic degradation of organic matters is described and this kind of electrode material was successfully applied to actual industrial ultra-high chemical oxygen demand (COD) organic waste water treatment.Diamond film with different quality was prepared by hot filament chemical vapor deposition(HFCVD) , microwave plasma chemical vapor deposition (MPCVD)and DC plasma jet chemical vapor deposition (DC plasma jet CVD). Besides high doped Si, diamond was successfully deposited on metal substrates with relatively high conductivity such as Ta, Ti, Nb by CVD method. Raman spectroscopy, X-ray diffraction(XRD), and scanning electron microscopy(SEM)examinations demonstrated that the films had well-defined sp3 bond diamond features. Only very little non-diamond was found. The deposition conditions such as power, pressure and the concentration of carbon source effect on the quality of the diamond film were investigated.The electrochemical behaviors of Ta/BDD electrode were investigated using cyclic voltammetry and AC Impedance and electrode / solution model was proposed. It was found that characteristic voltammetry features of polycrystalline diamond electrodes deposited on Ta(Ta/BDD) in Na2SO4 solution were a wide potential range for water stability (4.1 V (-1.8 V~+2.3 V vs. Saturated calomel electrode)) and low background current. A much higher oxygen evolution potential of Ta/BDD electrode was obtained than the other electrode such as Pt,IrO2,RuO2. The effect of PH value and amount of carbon source in CVD deposition process to the BDD potential window were studied. Impedance characteristics of Ta/BDD under different polarization voltage were investigated by AC impedance measurement and equivalent circuit was used for the simulation.Electrochemical degradation of wastewater containing phenol and nitrophenol on Ta/BDD was studied. It was observed that both the two organic pollutant can be oxidation efficiently within a specified time, with pollutant and COD removal efficiency as high as 100%. The effect of current density,organic initial concentration,support solution and its concentration on the electrocatalytic degradation have been investigated. It was found that Ta/BDD anode provided a higher oxidation rate and higher current efficiency than conventional electro-catalytic electrodes PbO2 in the degradation of phenol. Good electrochemical stability of Ta/BDD electrode was obtained in the accelerated life test. XRD tests showed that electrode surface unchanged for a long time in the electrolysis process. According to the results, Ta/BDD anode were seen to be a unique electrode for the degradation of organic and COD simultaneously.BDD electrodes were assembled and used for ultra-high COD wastewater degradation. High-efficiency and low-power consumption were obtained in the catalytic degradation of monosodium glutamate and rubber industrial wastewater, proving BDD is an ideal electrode to electro-catalytic depredate of organic wastewater with ultra-high COD.